A boom type aerial refueling system is used in a military aerial tanker aircraft known as the Boeing KC-135. This boom is supported from the rear lower surface of aircraft via a mount that is free to pivot about a fixed vertical axis for free pivotal movement in a sideward or azimuth direction. The boom is also supported for free pivotal movement about a lateral axis for up and down elevation movement. The boom contains a telescoping tube or duct with a nozzle for engagement with a receiving aircraft. The telescoping tube can move in and out of the boom to adjust for fore and aft movement of the receiving aircraft. A pair of aerodynamic control surfaces referred to as ruddevators are coupled to the boom to move the boom about the vertical and lateral axes. For instance when the ruddevators are moved collectively to a negative angle-of-attack, the boom will be moved downwardly; and a differential change in the angle-of-attack of the ruddevators will move the boom sidewardly.
The ruddevator angles of attack are controlled by actuators, which can be driven by pantographing cable or fly-by-wire control systems. The control systems may be operated by a variety of control signals including electrical, hydraulic, optical or mechanical signals from a boom operator. The operator is typically a human controlling the ruddevator position by providing the control signals, but the operator may also be an autonomous system relying on sensors monitoring the position of the two aircraft and the position of the boom and using a logic system providing the control signals to the control system. The control system commands the actuators to move the ruddevators and reposition the refueling boom. An advanced actuator control system may automatically position the ruddevators to adjust to movements of the boom that are induced by movement of the receiver aircraft instead of a boom operator's control. For example, when engaged with the boom the receiver aircraft can move the boom in elevation and cause the ruddevators to automatically adjust. Similarly when the receiver aircraft pulls the boom off to one side, the ruddevators will adjust accordingly. These adjustments to the ruddevator alleviate the forces that would be imposed on the boom and ruddevators as a result of the boom being displaced without any control input from the boom operator.
When performing an aerial refueling mission the rate of fuel transfer through the tanker boom (referred to as off-load) to the receiving aircraft is one of the limiting factors in off-load efficiency. Continuous positive contact with the boom and the receiving aircraft ensures fuel transfer. A refueling boom exhibiting substantially aligned refueling connection and positive control can increase positive contact duration between the tanker and the receiving aircraft and thus reduce the refueling mission time and ensure maximum and efficient fuel transfer. While aerial refueling using a boom-type fuel transfer system offers greater fuel transfer rates over other fuel transfer systems such as hose and drogue types, nevertheless it is desirable to further improve and more particularly increase and extend the aerodynamic range and performance of the existing boom.